To lower the energy consumption is a major problem in the field of development of electrical devices these days. Many devices are operated uninterruptedly for comfort reasons but also from the necessity of an associated operating reliability. This means that these devices are not switched on only when they are needed but are in operation uninterruptedly. This is necessary particularly if the device is a wireless receiving device in the case of which it is not predictable when it should receive an information item or an information item is sent out for reception.
Applications for this purpose are, for example, devices which are used for monitoring sensors which, when an event occurs, transmit the presence of this event and/or also associated additional information. The necessity for saving energy is given particularly when the wireless receiving device itself is not connected to a voltage supply system. In such a case, battery operation or similar autonomous power supplies are used, as a rule. To operate such devices, it is, therefore, now normal usage to place them into a so-called rest state in that parts of the device are switched off for reducing the energy consumption and are “woken up”, i.e., reactivated, as soon as the device is needed.
In this respect, a device with mode of operation switch is known, for example, from EP2572539 B1, also published as U.S. Patent Publication No. 2013/0130636 A1. This has a detector circuit which is configured for minimum energy consumption and monitors the presence of a predetermined radio-frequency signal. In detail, this means that when a predetermined information item such as, for example, an address, is transmitted at a particular frequency, the detector circuit forwards a wake-up signal to a microcontroller which thereupon changes into its normal operating state. The “woken” microcontroller thereupon controls the further waking up of the electronic device. In the method described in EP2572539B1, the address to be detected by the detector is impressed on a 125 kHz signal by means of OOK modulation (On-Off modulation) and with this an 868 MHz carrier signal is modulated.
In principle, the device described operates satisfactorily, but has the disadvantage that it is sensitive to interference signals. This means that the spacing between useful signal and interference signal is reduced with increasing distance between transmitter and receiver.